The present invention relates to an electric machine. Beyond this the present invention relates to a method for cooling an electric machine.
To enable electrical machines to be cooled efficiently in operation, corresponding coolant circuits are provided. Electrical machines which are embodied for example in accordance with cooling type IC 611 have an inner coolant circuit with an inner fan and an outer coolant flow with an outer fan, which can be thermally coupled via a heat exchanger. With electrical machines having two fans which are connected to the shaft of the electrical machine, these fans create an axial force on the rotor as a whole. This force, which is created by the fans in the axial direction of the electrical machine, occurs in particular with rapidly rotating electrical machines. The axial force is additionally increased if, instead of two radial fans, one radial fan and one axial fan are used for example. If the magnetic resetting force which is created by the stator or the laminated core of the electrical machine is smaller than the axial force exerted by the fans, the entire rotor moves away from its geometrical center. With electrical machines which have a fixed bearing, the rotor moves by the play in the fixed bearing until it stops and then imposes an additional axial force on the fixed bearing. This problem also occurs with electrical machines which have a floating bearing for example.
To address the aforesaid problem, in no-load tests of such electrical machines, rotor holder facilities are used in order to hold the rotor in the geometrical center. A further option consists of imposing a high axial force on the fixed bearings in operation of the electrical machine. Furthermore it is known, with electrical machines which have two fans on a common shaft, to embody the fans so that their directions of conveyance are aligned in opposing directions. Thus for example a vertical electrical machine is known in which the outer fan is disposed rotated by comparison with the inner fan. This enables this electrical machine to be protected from rain or moisture since the coolant is sucked into the fan housing from below.
With such electrical machines the problem also exists of high levels of noise developing from the fans. In addition there is the danger that with the outer coolant flow the heated exhaust air will be sucked in again via the inlet opening of the fan housing of the outer fan.